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A chemical linked to widely used agricultural fungicides and commonly found as a residue on food may be associated with girls starting their periods earlier, according to new research from Spain.
The study, published in Environmental Research, tracked 506 girls from the long-running Spanish INMA (Environment and Childhood) project and found that higher levels of a pesticide-related chemical called ethylene thiourea (ETU) were linked to an increased likelihood of earlier menarche, the first menstrual period.
Researchers measured pesticide metabolites in urine samples collected when the children were between 7 and 10 years old and then followed them until adolescence.
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The team examined markers of exposure to several modern pesticides, including insecticides and fungicides that can act as endocrine-disrupting chemicals, substances that interfere with the body's hormones.
Earlier puberty has become a growing public health concern. Menarche now typically occurs between ages 12 and 13 in many countries, and research suggests the age has fallen markedly over the past century.
Early puberty has also been linked to a higher risk of metabolic, cardiovascular and mental health problems later in life, as well as some hormone-related cancers.
The strongest finding involved ETU, a breakdown product of ethylene-bis-dithiocarbamate fungicides such as mancozeb.
Girls with higher ETU levels were 32 to 39 percent more likely to experience menarche during the follow-up period than those with undetectable levels.
What Foods Could Be Affected?
ETU is a breakdown product of fungicides such as mancozeb, which have been widely used on crops including grapes, tomatoes, potatoes, apples and citrus fruits.
Modern pesticides are also used in some non-agricultural settings, but food remains the main source of exposure for the general population, researchers said.
The average age at menarche among girls who reached the milestone during the study was just over 12 years old, although ages ranged from 9 to 15.
Interestingly, the researchers also identified an association in the opposite direction for another pesticide marker.
Girls with detectable levels of TCPy, a metabolite linked to the insecticide chlorpyrifos, tended to reach menarche later than girls with undetectable levels. The reasons for this finding remain unclear.
The authors stressed that the findings do not prove pesticides directly cause earlier puberty.
While there are biological explanations that could account for the association, including possible effects on thyroid hormones and reproductive signalling pathways, the study was observational and cannot establish cause and effect.
They also highlighted several limitations, including the fact that pesticide exposure was estimated from urine samples taken at a single point in childhood.
Because these chemicals leave the body relatively quickly, a single measurement may not perfectly reflect long-term exposure.
Still, the researchers say the study provides some of the first prospective evidence linking exposure to modern non-persistent pesticides with the timing of puberty in girls.
They called for larger studies to determine whether the findings can be replicated and to better understand how exposure to pesticide mixtures may affect developing children.
Reference
Freire, C., Olivas-Martinez, A., Castiello, F., Jimeno-Romero, A., Lopez de Calle, S., Suárez, B., Tardón, A., Rodriguez-Suarez, M.M., Guxens, M., Vrijheid, M., Beneito, A. and Lopez-Espinosa, M.-J. (2026). Age at menarche and exposure to non-persistent pesticides in Spanish girls from the INMA (environment and childhood) project. Environmental Research, [online] 300, p.124450. doi:10.1016/j.envres.2026.124450.
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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